The present invention relates to the regulation of the fuel gas supply to a domestic heating appliance by means of a flow control valve which is operated by an electric motor, modulating the flow in response to the variations in temperature of the heated area, and the valve is the dual seat lift type.
FR-236742 discloses a gas flow control valve for a domestic gas boiler, wherein the flow of gas supplying the burner is regulated by means of the gradual opening of a valve hole in accordance with the temperature of the water supplied by the boiler, in three stages: minimum flow, gradual flow and maximum flow. The regulation valve has two series valve members coupled to a single valve stem, inside an internal gas chamber, which communicates the gas inlet pipe with the outlet pipe. The valve stem slides axially actuated by an electromagnet in accordance with the value of the electric current applied to the winding. The valve member for minimum flow is moved first of all to open a central through hole and it is mounted on the same stem as the high flow valve member. It is then lifted from its valve seat in a second gradual movement to let the high flow pass. For closure, each valve sealing member is forced in the opposite direction by its respective return spring.
U.S. Pat. No. 4,085,921 discloses a multi-mode gas control valve for a heating appliance, such as a water heater. The valve has a single seat and the sealing member takes the form of a flat disc, the flow opening being variable depending on the separating distance of the sealing member. In accordance with the variation in the value of the water temperature measured by a sensor, the valve control unit generates an analogue signal that supplies the actuating electromagnet to maintain the valve in different operating modes, with a minimum constant gas flow, a gradual intermediate flow, and a constant maximum flow.
EP-691495-A discloses a gas control valve for a heating appliance of the type with an axially sliding stem with a dual valve seat. The sealing members are in series in a single gas chamber between the inlet and outlet pipes and are provided with a respective spring mounted on the stem. The valve is operated by means of an auxiliary electromagnet with a sliding armature for opening and closing both valve passages, and a stepped motor for graduating valve opening according to an operating mode, which modulates the flow of gas supplied to the heating appliance, making use of an associated electronic control unit and various sensors.